In a commercial process for forming an alloy on the surface of a substrate, an electrode which is formed of the allowing material is connected to a pulse generating machine to create repetitive spark discharges between the electrode and the substrate while the electrode is in engagement with the substrate. The electrode may be rotated while in engagement with the substrate and caused to traverse the surface of the electrode to distribute the alloying material over the surface of the substrate. In this commercial process, it is believed that small amounts of the electrode material melt during each discharge and are transferred to the substrate. The discharge is also effective to either melt, soften or otherwise create a condition for alloying at the surface of the substrate so that the electrode material forms an alloy with the substrate material at the zone contiguous with the surface.
To create the repetitive spark discharge, the electrode must be energized with an electric potential. In the past use of this process, a suitable electric potential has been between 110 and 165 volts.
By virtue of recent regulatory actions, a 50 volt limitation has been imposed on equipment such as the above surface alloying apparatus. Particularly, recent regulations specify that an operator who inadvertently contacts the probe must not be exposed to a potential of greater than 50 volts. Of course, it is possible to merely step down the operating voltage of the apparatus from past voltage levels to less than 50 volts. However, applicants have discovered that an operating voltage of less than 50 volts results in a substantial reduction in performance of the apparatus.
In accordance with the present invention, applicants have provided a safety circuit for surface alloying apparatus and the like which preserves the performance of the apparatus and yet exposes the operator to a minimal voltage on the electrode should the operator inadvertently contact the electrode. The safety circuit can be implemented with a minimum number of components and alternations to pre-existing circuits, and hence, provides an extremely effective yet low cost solution to the problem posed by the new regulations.
According to applicants' invention, the firing circuit which connects the electrode to the source of electric potential to create the spark discharges is enabled only when the electrode is in electrical contact with the workpiece. This has been accomplished by providing a triggering circuit which incorporates the workpiece and the electrode so that the circuit which supplies a triggering pulse to the triggering device is completed only when the electrode is in engagement with the workpiece. Hence, prior to the electrical connection of the electrode and the workpiece by engagement therebetween, the triggering circuit is not completed so that triggering cannot be accomplished. When the electrode and the workpiece are electrically engaged, the triggering circuit is completed so that triggering will occur and the process can proceed. When the process is in operation, the engagement between the electrode and the workpiece itself receives the high potential discharges of the electrode and thereby protects the operator.